Show rollback-specific strings for users during/after rollback happens

Change text on the update screen:
- During rollback:
    "Your administrator is rolling back this device (25%)"
    https://screenshot.googleplex.com/WrMrGxdOU86.png
- After rollback:
    "Your administrator rolled back this device. Please save important
     files, then restart. All data on the device will be deleted."
- Button text:
    "Restart and reset"
    https://screenshot.googleplex.com/Zq2QsMTXUdt.png

Change text of the notification:
- https://screenshot.googleplex.com/vVdBEHcKzKR.png
- Title:
    "Device will be rolled back"
- Text:
    "Your administrator is rolling back your device. All data will be
     deleted when the device is restarted."
- Button:
    "Restart and reset"

Notification is also shown at warning level.

Bug: 863088
Change-Id: I99cd590fee90d7ac1ad5927b3459f9cb97a051a1
Reviewed-on: https://chromium-review.googlesource.com/1143481
Commit-Queue: Marton Hunyady <hunyadym@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576922}
23 files changed